Technical Service Bulletin:
A3 / E3 Error Code Troubleshooting
Models: C1210ESC, C1210ES, C1050ES, C950ES, 940ES, 940ESO, 830ES
The following procedures are for gathering information to assist
Bosch Tech Support in determining the cause and solution to the
problem. Unplug power cord and remove outer and inner covers
from heater (refer to Installation Manual).
Note: The following bulletin applies only to serial numbers up to
Error code explanation:
A3 error code: Open jumper circuit
E3 error code: Incorrect resistance in jumper circuit
Phillips head screwdriver
1. Check position of jumper at top right of heat exchanger plugged
into connector on green wires (Fig. 1, pos.1).
If jumper is near heat exchanger or ﬂ ue gas collector, move
jumper to the right and tuck wires into clip on right side to
prevent jumper from overheating (Fig. 2, pos. 1).
2. Check that jumper is connected tightly to connector. Disconnect
and reconnect to improve connection.
3. Check for correct appliance type setting (model 830ES skip this
a. Plug in heater's power cord and place heater into diagnostic
mode (refer to manual section 6.7).
b. Push "+" button until "P7" is displayed.
c. Push "P" button. Display should read "NO" or "NC".
d. If display reads "Cd", push "+" button until "NO" is dis-
played. Push "P" button for 5 seconds to save correct
e. Push power button to "off" position and back to "on"
Before proceeding to the next step, plug in power cord and reset
the heater to see if error code has cleared. If error code will not
clear or occurs again during operation, move to step 4.